The present invention relates to room-temperature setting silicone composition for taking dental models (silicone impression material) including as fundamental components (a) an organopolysiloxane having in its molecule at least two vinyl groups and (b) an organohydrogen polysiloxane having in its molecule hydrogen atoms bonded to at least two silicone atoms, and further including (c) a known platinum-based catalyst, (d) hydrophobic fillers, and (e) finely divided palladium and/or a finely divided palladium alloy containing more than 10% by weight of palladium, and a method of using the same.
Heretofore, the organopolysiloxane-based material for taking dental impressions has widely been used as a silicone impression material. More particularly, such a material employs a dihydroxy polyorganosiloxane as a base, an alkyl silicate or polyalkyl silicate as a cross-linking agent and an organic tin compound as a condensation catalyst, which are mixed or kneaded together to effect a condensation reaction therebetween, thus forming an elastomer. However, such a system is disadvantageous in that the elastomer evolves volatile components such as alcohols produced in the condensation reaction and unreacted alkyl silicate to undergo a gradually increasing change in dimensions upon setting, and still gives out an offensive odor peculiar to the liquid catalyst.
Currently, a system for producing elastomers from organopolysiloxanes each having in its molecule vinyl groups and organohydrogen polysiloxanes each having in its molecule hydrogen atoms bonded to silicone atoms by setting them by an addition reaction with the aid of a catalyst at room temperature has been developed and found to have marked advantages over the prior art silicone impression materials. That is to say, this silicone impression material undergoes a linear shrinkage in the order of only about 0.1%, i.e., about one-fourth to one-tenth or less of that of the conventional silicone impression materials 24 hours after an impression has been taken. Accordingly, it is possible to prepare a model having a high dimensional accuracy. In addition to their tasteless and odorless, the organopolysiloxanes having in their molecues vinyl groups and the organohydrogen polysiloxanes having in their molecules hydrogen atoms bonded to silicone atoms can be mixed and kneaded in equal amounts as their silicone polymer paste products have the same viscosity. From this fact, they are found to excel in dental performance and workability.
In the reaction process during which the organopolysiloxanes having vinyl groups and the hydrogen atoms of the organohydrogen polysiloxanes are subjected to an addition reaction to form elastomers, however, hydrogen gas is partially evolved. When a gypsum slurry is poured into an impression just after the impression has been taken, a number of pores are formed on the set gypsum model due to the hydrogen gas, thus producing a spongy surface thereon. In most cases, such a model was not substantially available to practical dentistry. In order to prevent such a spongy surface from being formed on the gypsum model by the hydrogen gas, it was required to pour a gypsum slurry into a silicone impression taken after the impression has been allowed to stand for more than 2 hours, has been degassed by heating, or has been treated under reduced pressure for more than 5 minutes. This operation was troublesome in making the model, and wasted much time. Furthermore, this operation did not only require a special device, but resulted in a fear that the dimensional accuracy of the model is made worse.